Pau d'arco is derived from the inner bark of a giant hardwood tree that is native to the Amazon rainforest in South America. It is a tree with extremely hard wood, its name is the Portuguese word for “bow stick,” an appropriate term considering the tree’s use by the native South American Indians for making hunting bows. The bark and wood are used to make medicine. Though possibly unsafe, especially at higher doses, pau d'arco is used to treat a wide range of infections. These include viral respiratory infections such as the common cold, flu, and H1N1 (swine) flu; sexually transmitted infections such as gonorrhea and syphilis; infections of the prostate and bladder; ringworm and other parasitic infections; yeast infections; and infectious diarrhea. Pau d’arco is also used for cancer. Interest in this use was intensified by extensive research in the 1960s that focused on the possible anti-cancer activity of lapachol, one of the chemicals in pau d’arco. However, research studies were stopped because, at the amounts needed to be effective against cancer, pau d’arco might well be poisonous.